Heatsink Requirements - Philips TDA8920B Manual

Philips Semiconductors

13.5 Heatsink requirements

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Preliminary data sheet
If two or more class-D amplifiers are used in the same audio application, it is strongly
recommended that all devices run at the same switching frequency. This can be realized
by connecting all OSC pins together and feed them from an external central oscillator.
Using an external oscillator it is necessary to force pin OSC to a DC-level above SGND for
switching from the internal to an external oscillator. In this case the internal oscillator is
disabled and the PWM will be switched on the external frequency. The frequency range of
the external oscillator must be in the range as specified in the switching characteristics;
see Section 12.1.
In an application circuit:
•
Internal oscillator: R
•
External oscillator: connect the oscillator signal between pins OSC and SGND; delete
R and C .
OSC OSC
In some applications it may be necessary to connect an external heatsink to the
TDA8920B. Limiting factor is the 150 °C maximum junction temperature T
cannot be exceeded. The expression below shows the relationship between the maximum
allowable power dissipation and the total thermal resistance from junction to ambient:
T – T
( )
j max
R = ----------------------------------- -
( )
th j a –
P
diss
P is determined by the efficiency (η) of the TDA8920B. The efficiency measured in the
diss
TDA8920B as a function of output power is given in
be derived as function of output power (see
The derating curves (given for several values of the R
A maximum junction temperature T
maximum allowable power dissipation for a given heatsink size can be derived or the
required heatsink size can be determined at a required dissipation level.
connected between pin OSC and V
OSC
amb
= 150 °C is taken into account. From
j
Rev. 01 — 1 October 2004
2 × 100 W class-D power amplifier
SSA
Figure 21.The power dissipation can
Figure 20).
) are illustrated in
th(j-a)
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
TDA8920B
which
j(max)
(5)
Figure 8.
Figure 8 the
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